Anode block for magnetrons



Feb. 25, 1958 L. R. WALKER ANODE BLOCK FOR MAGNETRONS Filed Feb. 21, 1946 INVENTOR. LAURENCE R. WAL

KER

ATTORNEY AN ODE BLOCK FOR MAGNETRONS Laurence R. Walker, Cambridge, Mass., assignor, by mesne assignments, to the United States of America as represented by the Secretary of the Navy Application February 21, 1946, Serial No. 649,418 3 Claims. c1; ens-39.75

The present invention relates to apparatus for damping the undesired resonant modes of a high frequency oscillator, and more particularly to such apparatus adapted to use with multicavity type magnetrons.

It is well known that multi-cavity magnetrons will oscillate in a number of modes other than the desired one. In a magnetron, for example, having an anode block with 16 vanes and as many separate cavity resonators, the desired mode is that which causes alternate vanes to be simultaneously at maximum positive potential while the remaining vanes are all at maximum negative potential. In this mode, it can be seen that there are eight complete electrical field cycles around the circular anode block, and that there is a phase angle of 7r radians, or 180 degrees, between the fields at adjacent vanes. The desired mode is thus appropriately called either the 1r or the n=8 mode in the case of the 1-6 resonator anode under discussion.

The next prominent mode in the 16 resonator magnetron is the n=7 mode, wherein there are seven complete field cycles about the circular anode block instead of eight. If not loaded, the n=7 mode breaks into steady oscillation prior to the desired mode, causing mode jumping. The present invention concerns generally apparatus which causes dissipation of energy of the undesired n=7 mode without disturbing the desired one.

A specific object of the present invention is to provide a means for attenuating only the unwanted modes in a magnetron.

Another object is to provide such selective magnetron demoding by the use of a half-wave slot disposed in one of the magnetron resonators.

A further object is to provide a selective magnetron demoding means which is simple to construct and which has mechanical stability.

These and other objects are made apparent in the following specification and illustrated in the accompanying drawing which is a partially cut-away perspective view of one form of magnetron anode of the present invention.

The principle of the selective dissipation of mode energy within a magnetron as disclosed in this invention is based upon the differences in the space distribution of energy of the two modes concerned. The desired 1r mode efiectively concentrates its energy in a single standing wave having a point of maximum intensity located in each of the cavity resonators. The n=7 mode, however, may be resolved into two distinct voltage standing waves, namely, a sine and a cosine wave, 90 out of phase with respect to each other. Due to the symmetry of the 1r mode standing wave relative to the physical configuration of the magnetron anode, this wave remains fixed in its geometrical orientation despite the introduction of a structural and electrical discontinuity or asymmetry to the magnetron resonators. In contradistinction, the two 12:? mode standing waves, although they always remain in fixed relation to one another, orient themselves at random if the magnetron has absolute circular symmetry.

In all magnetrons, a means is provided for coupling United States Patent 1 'one component of the undesired n=7 mode.

out radio. frequency energy, and is usually associated with one of the cavity resonators. The asymmetry-introduced by this coupling, although verysmall, is sufiicient to lock into position, or key, the n=7 standing waves in the magnetron, one of the waves aligning itself so as to have maximum output coupling and the other, so as to have zero coupling.

An undesired situation can be seen to exist, wherein the desired 7:" mode which experiences maximum output coupling is attenuated in the magnetron load along with maining n=7 mode wave is left unattenuated in the magnetron and the deleterious moding ettect cited above is the result.

Apparatus of this invention alleviates these difficulties by introducing a second discontinuity which is more prodominant than the first so that the 11:7 mode waves will lock or key themselves on this rather than on the asymmetry introduced by the output coupling loop. With the two n=7 mode standing waves keyed on the second asymmetry, the maximum point of one of the waves and the zero point of the other being locked in position thereat, both of the undesired standing waves are caused to be attenuated by placing the second, keying discontinuity at such a position in the magnetron relative to the output loop that the two waves are so located at the loop as to be coupled equally out to the magnetron load. The desired 1r mode is unaffected by the introduction of the second asymmetry and is no longer troubled by an excessively large undesired mode resonating freely without attenuation.

The accompanying drawing shows a preferred embodiment of the magnetron structure of the present invention. It will be noted that the conventional axial cathode, the magnetron envelope, anode straps and the means for producing an axial magnetic field are not shown. In this figure is shown a magnetron anode block 10 having machined therein 16 identical cavity resonators 11. A conventional coaxial output lead 12 has its coupling loop 13 mounted in one of the resonators 11. This loop 13 thereby introduces a small asymmetry to the magnetron anode.

Mounted in another of the magnetron resonators 11 at a predetermined angular distance from the output coupling is a second asymmetry, strongly predominant over the first, in the form of an axial and radial slot 14 which extends through the full thickness of the anode block 10. The slot 14 is effectively in length (Mr being the wavelength of energy of the desired 1r mode), and is terminated by the short circuited end wall 15 formed in the anode block. The slot 14 thus has no efiect upon energy of the 11' mode, but does present an appreciable discontinuity to the n=7 mode, locking the latter in the desired position.

For compactness, the slot 14 may be cut at a skew angle or may be made curved or with a sharp break, as for example, the slot 16 indicated in the figure by the broken lines. The present invention is not limited to the specific slot-type asymmetry described but may include any number of structures capable of inserting into the magnetron a similar discontinuity.

The invention described in the foregoing specification need not be limited to the details shown, which are considered to be illustrative of one form the invention may take.

What is claimed is:

1. In a magnetron, a magnetron anode block adapted to attenuate energy in undesired modes of oscillation in Patented Feb. 25, vs-

The re- V n m mas v said" magnetron,- sa ictlanode; block being" forrned with a i V multiplicity of substantially identical axial-cavity. resona-j r V ,tors arranged in 'a circle andspacedat equLangular' dis:

tances about the center'of said circle, said anode block 7 'being further. formed withfan axiahslot substantiallyson:

' halfiwave length. long at'fthe: frequency'iof the desired f mode of oscillation of said. magnetron; s'aidzslot being terminatedat one end by saidtanode 'bl'ockzandiiat the other: end thereof by the cavity' io'f one of said cavityg res onators.

2. Apparatus attenuatinglthe'degenerate-niode' V Y Nir iiii, V V

' in {a niagnetroiios'cillator haying; N cylindrical cavity resonators sn't-roundin a centfialdnter'action space com rising a radialslorextendingfrom i redterminedlone f of said cylindrical cavity resonators, other thanitlif output" CiaVifY .fe'SDfiiiGi 6f SE ilCl magnetrbmjsaid :Sldtfbifig l bounded onan' sides by surfacs'df saidfanode bloc nd mode, wherehy' said slot presents substantially. gzero fresistance't'ojthe desired mode andfa substantialreact'attce tothe degenerate rhode, and whereby said degenerate a mode is .locked' on saidipredeterminedcavityresbnator;

said predetermined cavityresonatorbeingv so located with respect to said output cavity resonator Ytha tfegualamounts of" the quadrature wave components, of the degenerate i made. arecoijpledfto' the output cavity resonator and thereby "attenuated;

s and the"leng'th" cif1said'' wavelength of V 1 Apparatus for attenuating the degenerate niode V '20 resonatonzthelocation:offsaidipredetermin'ed;eayityxes onatorl with respect'to' saidroutputadavitysresonatorrbeing f such that equal amODHI S -OfETthBT quadratureiwayeicom ponents: of theidegenerate? mode: are coupled to the outf put-cavity resonatorza'nd therebyiattenuated H B L AT WATB I Referncesfiitedinttheafillirflthistpatenfiz r '7 mode whereby saidslot actsas a'low 'resistance to the r r desired mode and as a substantialreactanceto'the de-'* generate mode and whereby said degenerateJrnQde is" i 5 spatially fixed twitharespeotztoasaidzrpredetrmined .caiiy 

